Method of printing



Patented May 8, 1945 UNITED STATES 2,375,660 PATENT OFFICE 2,375,660 rETHOD OF PRINTING Wilbur -L. Jones, New York, N. Y., assignor toInterchemical Corporation, New York, N. Y.,

a. corporation of Ohio No Drawing.

Application December 26, 1941, Serial No. 424,415

4 claims. (Cl. 101-170) tendency to offset and smudge than printsproduced by former methods.

Printing with thermoplastic or hot melt inkshas certain obviousadvantages over printing cold with conventional inks and has beenreceiving considerable attention recently. At present such inks havebeen printed both by the typographic and gravure methods. In printing bythe latter method with inks that have lateraly been developed,commercially acceptable results have been obtained, but therenevertheless have been certain limitations, due primarily to thethickness of the film laid dow I have found, for example, that while theappearance of prints produced with an ordinary gravure cylinder isacceptable in the areas of half-tone, the areas of solid color containnoticeable mounds of ink where the flow-out has been incomplete beforecooling and solidification of the ink. The film is also thick enough sothat there is a pronounced tendency for the prints to offset if storedin a warm room or rewound before the web and ink are entirely cool.Furthermore, due to the thickness of the film, it is somewhat difl'icultto obtain drying or cooling quickly enough altogether to preventoil'setting, and this obviously limits the ultimate speed at which theprinting can be carried out.

I have now discovered that all of these difficulties or limitations inthe gravure method of thermoplastic printing can be successfully over-40 come, and at the same time the process can be rendered far moreeconomical, by (1) printing with anintaglio or gravure cylinder in whichthe depth of the engraved cells is approximately one third to one halfof that normally used and (2) employing an ink which has sufileientpigment to hide the paper properly and with suitable color efl'ect infilm thicknesses of from 5 to 15 microns but in insuificient quantity toproduce a yield value of over 100 dynes per square centimeter at 0temperatures at which the ink is printable. The

term "yield value? as used herein refers to a tan.-

gential force (measured in dynes per square centimeter) equivalenttothat acting upon an area of one square centimeter that will just producea flow of a plastic at an infinitely slow rate relative to an area ofone square centimeter parallel to the first area and spacedperpendicularly therefrom by a distance of one centimeter.

Thus, the practice of my improved method of to 'fore, produced and usedcylinders which have a cell depth of 20 to 30 microns in the areas whichproduce solid color, as compared with conventional intaglio cylinderswhich have a cell depth,

in the areas which produce solid color, of from I 40 to microns.Cylinders etched in accordance with my invention are so shallow thatsolid colors cannot be deposited from them when conventional solventintaglio inks are used.

However, it should-be understood that the reduction in the depth of thecells of the intaglio cylinder alone, with consequent reduction in thethickness or the applied film, for the attainment of my improvedresults. My experiments have shown that if the depth of the cells isreduced in the areas of solid color and ordinary thermoplastic inks areemployed, proper coverage and colorintensity cannot be obtained.Therefore, it is necessary to increase the pigmentation of thethermoplastic inks to a point where proper coverage and color. intensitycan be obtained with the reduced film thicknesses. I have found that ifthermoplastic inks are very highly pigmented, so as to producesatisfactory prints in films of the order of 5 microns to 15.

microns in thickness, the tendency to transfer .in piles issubstantially reduced. This is due to the fact that the very thin filmhasa tendency to adhere to the paper on which it is printed, and

there is insufiicient film to produce an eifective transfer. However,there is a critical upper limit on the amount of pigment that may beaddedsince too high a pigmentation may introduce undesirable yield valueinto the ink compositions and this will produce unsatisfactory fiow-out.

25% of iron blue may be used; and the limits the conventional is notsuflicient rise't'o airange of from 30 to 50% for chrome yellow.

Thermoplastic inks of the general character disclosed in my copendingapplication Serial No. 244,607, filed December 8, 1938, may be used inthe practice of my improved method. Typical examples of such inksincluding the particular pigments referred to above are as follows:

EXAMPLE 1 Monotone yellow ink Parts by weight Chrome yellow 35Hydrogenated castor oil: (M. P- 183 F.) 51

Grinding varnish comprising: Gum rosin (W. W. grade), 50% Raw linseedoil, 50%

The pigment is introduced into the ink by dis persion into the grindingvarnish. This ink has a melting point of about 180 F., and at atemperature of 210 F. has a' viscosity of 0.8 poise and a yield value ofabout '7 dynes per square centimeter. When chilled, it is printable toabout 170 F. -It is an excellent ink for printing of monotone yellows.

EXAMPLE 2 Process blue Parts by weight Iron blue 20.0 is ground in avarnish comprising Linseed oil and Alkyd resin (see below) and the pasteis mixed with Hydrogenated castor oil 56.6

The alkyd resin in the above ink may be prepared by reacting, at 475 F.,150 parts by weight of the dfloasic acid obtained by reacting molarproportions of dipentene and maleic anhydride, 150 parts of theunsaturated fatty acids obtained by the dehydration of castor oil acids,'70 parts of glycerol, 3 parts of lauryl alcohol and 292 parts ofmodified rosin ester gum (modified with 20 per cent. of phenol aldehyderesin in known manner) to the point where the resin has an acid value of9 to 10, and a melting point of 165 F.

This ink has a melting point of 185 F., and is printable at 170 to 175F. At a temperature of 195 F., the ink has a viscosity of 1.0 poise anda yield value of 4 dynes per square centimeter. This is an excellentprocess blue, as I have found that best results are obtained when blueprocess inks have melting pointsabove 160 F., and are printable below1'75" F.

EXAMPLE 3 Monotone black Parts by weight Carbon black 6.0 Gilsonite 6.8Methyl violet toner 1.0 Zinc resinate 1.7 Petroleum base ink oil 14.0Hydrogenated soya bean oil 10.0 Candelilla wax 60.5 F. At

This link has a melting point of 160 amount of pigment in the ink mayvary from 6 to 25%; whereas, if the pigment has relatively poor hidingpower and low tinctorial value, such as is he case with yellows andother light colors, the amount required in the thermoplastic ink mayvary from 30 to50%.

What I claim is:

I l. A method of printing with thermoplastic inks which are solid atnormal room temperatures and become liquid when heated to elevatedtemperatures between 150 and 300 F. which comprises applying to anintaglio printing cylinder, having engraved cells with a depth of from20 to 30 microns in the areas of solid color, a thermoplasticprinting'ink comprising a thermoplastic vehicle and pigment insufficient quantity completely to hide paper in film thickness of from 5to 15 microns but in insufiicient quantity to produce a yield value ofover dynes per square centimeter at temperatures at which the ink isprintable; and transferring such ink from said engraved cells of theprinting cylinder to the material being printed.

2 A method of printing with thermoplastic inks which are solid at normalroom temperatures and become liquid when heated to elevated temperaturesbetween and 300 F. which comprises applying to an intaglio printingcylinder, having engraved cells with a depth of from 20 to 30 microns inthe areas of solid color, a thermoplastic printing ink comprising athermoplastic vehicle and from'8 to 50% of pigment, the ink having ayield value of less than 100 dynes per square centimeter at temperaturesat which the ink is printable; and transferring such ink from saidengraved cells of the printing cylinder to the material being printed.

3. A method of printing with thermoplastic ink which are solid at normalroom temperatures and become liquid when heated to elevated temperaturesbetween 150 and 300 F. which comprises applying to an intaglio printingcylinder, having-engraved cells wi h a depth of from 20 to 30 microns inthe areas of solid color, a thermoplastic printing ink comprising athermoplastic vehicle and from 6 to 25% of a pigment having good hidingpower and high tinctorial value; and transferring such ink from saidengraved cells of the printing cylinder to the material being printed.

l. A method of printing with thermoplastic inks which are solid atnormal room temperatures and become liquid when heated to elevatedtemperature between 150 and 300 F. which comprises applying to anintaglio printing cylinder, having engraved cells with a depth of from20 to 30 microns in the areas of solid color, a thermopla'itic printingink comprising a thermoplastic vehicle and from 30 to 50% of a pigmenthaving poor hiding power and low tinctorial value; and tlallSfBlILlgsuch ink from said engraved cells of the printing cylinder to thematerial being printed.

WILBUR L. JONES.

